1. Field of the Invention
The present invention relates to a rolling bearing with a sealing plate having a grease enclosed therein, which is used to form the rotary supporting portion of automobile auxiliary machineries to be installed in engine room such as alternator and compressor. In other words, the present invention is intended to improve the reliability and durability of a rolling bearing with a sealing plate having a grease enclosed therein which is used at high temperatures (e.g., 170xc2x0 C. or higher).
2. Description of the Related Art
In order to form the rotary supporting portion of various mechanical devices, rolling bearings with a sealing plate 1 and 1a as shown in FIGS. 1 and 2, respectively, are used. The rolling bearings with a sealing plate 1 and 1a each composed of an outer race 3 having an outer raceway 2 formed in the middle portion of the inner surface thereof, an inner race 5 having an inner raceway 4 formed in the middle portion of the outer surface thereof, and a plurality of rolling elements rotatably provided between the outer raceway 2 and the inner raceway 4. Provided extending between the both ends of the inner surface of the outer race 3 and the both ends of the inner race 5 is a sealing plate 7a or 7b. The sealing plate 7a or 7b blocks the both axial opening ends of a space 8 defined by the inner surface of the outer race 3 and the outer surface of the inner race 5 having the rolling elements 6 provided therein. A grease is enclosed in the space 8 between the pair of sealing plates 7a or 7b to lubricate the area at which the outer raceway 2 and the inner raceway 4 come in rolling contact with the rolling surface of the rolling elements 6.
The sealing plates 7a and 7b each comprise a circular core metal 9 formed by a metal plate such as steel plate, and an elastic material 10a or 10b provided covering the core metal 9 and reinforced by the core metal 9. The inner and outer edges of the elastic materials 10a and 10b radially protrude beyond the inner and outer edges of the core metal 9. The sealing plates 7a and 7b engage the elastic materials 10a and 10b, respectively, with a stop groove 11 formed on the both ends of the inner surface of the outer race 3 so that they are supported at the both axial ends of the space 8. The inner edge of the elastic material 10a shown in FIG. 1 comes in sliding contact with a part of the surface of the inner race 5 while the inner edge of the elastic material 10b shown in FIG. 2 is closely opposed to a part of the surface of the inner race 5. In other words, the sealing plate 7a shown in FIG. 1 is a contact type seal while the sealing plate 7b is a non-contact type seal.
As the grease to be enclosed in the space 8, which constitutes the rolling bearing 1 or 1a having a grease enclosed therein, and the elastic material 10a or 10b, which constitutes the sealing plate 7a or 7b, respectively, there have been heretofore used usually the following materials (1) to (5).
[Grease]
(1) Urea-based grease comprising as a thickening agent a urea compound comprising isocyanate and amine and as a base oil comprising PAO and ether singly or in admixture;
(2) Fluorine-based grease having excellent high temperature characteristics;
[Elastic Materials 10a, 10b]
(3) Acrylic rubber obtained by the polymerization of ethyl acryate;
(4) Fluororubber obtained by the copolymerization of vinylidene fluoride with hexafluoropropylene; and
(5) Fluororubber obtained by the copolymerization of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene
Heretofore, a grease selected from the group consisting of the foregoing materials (1) and (2) and a sealing plate 7a or 7b comprising the elastic material 10a or 10b, respectively, made of a rubber selected from the foregoing materials (3) to (5) have been properly combined to form a rolling bearing 1 or 1a with a sealing plate having a grease enclosed therein.
The foregoing combination of the grease and elastic material 10a or 10b made of the material which has been heretofore known cannot necessarily assure sufficient reliability and durability at high temperatures.
The combination of the fluorine-based grease (2) and the fluororubber (4) or (5) exhibits a sufficient heat resistance but exhibits an insufficient grease durability under high rate and high load working conditions. Accordingly, this combination is not suitable for the construction of the rotary supporting portion of alternator, compressor, etc.
Further, the combination of the fluorine-based grease (2) and the acrylic rubber (3) not only exhibits an insufficient grease durability under high rate and high load working conditions but also exhibits a deteriorated elasticity of acrylic rubber after prolonged use at high temperatures, causing the sealing plate 7a or 7b to show a deterioration of sealing properties. Accordingly, this combination, too, is not suitable for the construction of the rotary supporting portion of alternator, compressor, etc.
Moreover, the combination of the urea-based grease (1) and the acrylic rubber (3) exhibits a deteriorated elasticity (hardening) of acrylic rubber after prolonged use at high temperatures, causing the sealing plate 7a or 7b to show a deterioration of sealing properties. Accordingly, this combination, too, is not suitable for the construction of the rotary supporting portion of alternator, compressor, etc.
Further, the combination of the urea-based grease (1) and the fluororubber (4) or (5) exhibits a deteriorated elasticity of fluororubber due to the effect of urea compound at high temperatures, causing the sealing plate 7a or 7b to show a deterioration of sealing properties. Accordingly, this combination, too, is not suitable for the construction of the rotary supporting portion of alternator, compressor, etc.
As mentioned above, a urea-based grease, if used as a grease, exhibits an insufficient durability under high rate and high load working conditions in any case. The resulting rolling bearing with a sealing plate having a grease enclosed therein cannot be secured with a sufficient durability. The results of experiment made by the inventors in this respect will be described in connection with FIG. 3. The experiment was made with a deep groove ball bearing having an inner diameter of 17 mm, an outer diameter of 52 mm and a width of 17 mm. In some detail, this ball bearing was operated at a rotary speed of 18,000 r.p.m. at an ambient temperature of 180xc2x0 C. and a radial load of 150 kgf. Under these conditions, the time required until seizing due to mallubrication occurs was measured. As samples there were prepared two each for rolling bearing having a urea-based grease enclosed therein and rolling bearing having a fluorine-based grease enclosed therein, totaling four. As can be seen in FIG. 3, which shows the results of the foregoing experiment, the rolling bearing having a fluorine-based grease showed seizing in about 10 to 20 hours. On the contrary, any samples comprising a urea-based grease didn""t show seizing even after 500 hours. The experiment was terminated after 500 hours.
As can be seen in the results of the foregoing experiment, the grease to be enclosed in a rolling bearing with a sealing plate which constitutes the rotary supporting portion of automobile auxiliaries to be installed in engine room such as alternator and compressor is preferably urea-based. As previously mentioned, on the other hand, the combination of a urea-based grease and the conventional fluororubber (4) or (5) is liable to hardening of fluororubber at high temperatures that makes it difficult to secure sufficient sealing properties as previously mentioned. The results of experiment made by the inventors in this respect are shown in Table 1.
The experiment the results of which are set forth in Table 1 was carried out by embedding specimens of the foregoing rubbers (4) and (5) and acrylic rubber (3) which had heretofore been as elastic materials 10a and 10b for sealing plates 7a and 7b, respectively, in a urea-based or fluorine-based grease. The ambient temperature during experiment was 190xc2x0 C. The experiment time (embedding time) was 100 hours. After the lapse of 100 hours, the specimen was then withdrawn from the grease for visual observation. When an abnormality in external appearance such as swelling and damage occurs, it is represented by the symbol x. When no such an abnormality occurs, it is represented by the symbol ∘. The results are set forth Table 1 above. As can be seen in the experiment the results of which are shown in FIG. 3 and the experiment the results of which are set forth in Table 1 above, the grease to be enclosed in the rolling bearing with a sealing plate constituting the rotary supporting portion of automobile auxiliaries to be installed in engine room such as alternator and compressor is preferably urea-based and the elastic materials 10a and 10b for sealing plate 7a and 7b, respectively, having a good affinity for urea-based grease is an acrylic rubber.
However, if as the elastic materials 10a and 10b for sealing plates 7a and 7b, respectively, there is used an acrylic rubber, the acrylic rubber showed a drop of elasticity after prolonged use at high temperatures, making it difficult for the sealing plate 7a or 7b to provide sufficient sealing properties over an extended period of time as previously mentioned. Accordingly, the acrylic rubber, too, cannot be preferably used as the elastic material 10a or 10b for rolling bearing with a sealing plate.
It is an object of the present invention to provide a rolling bearing capable of securing sufficient reliability and durability even under high temperature, high speed and high load working conditions.